Hydraulic system

ABSTRACT

A hydraulic system has a high pressure supply line, a low pressure return line maintained at a pressure above the ambient pressure, and a plurality of subsystems connected between the supply and return lines. At least some of the subsystems individually include a selector valve and a hydraulically operated device. The selector valve is connected to the high pressure supply line and also to the return line, the latter connection being through a discharge line. The selector valve is also connected to the hydraulically operated device for diverting high pressure fluid thereto. A check valve is interposed in the discharge line for permitting fluid to flow from the discharge line to the return line, but not in the reverse direction, and consequently before fluid will flow past the check valve into the return line the pressure within the discharge line must equal that in the return line. Each subsystem of the foregoing nature further includes a shutoff valve which senses the return pressure in the discharge line and prevents high pressure fluid from being diverted to the hydraulically operated device when the pressure in the discharge line falls off. Accordingly, should the discharge line or any line in common with it rupture, the shutoff valve will close and the subsystem will be rendered inactive, thus preventing the loss of hydraulic fluid through the rupture when an attempt is made to operate selector valve of the ruptured subsystem. A substantial loss of hydraulic fluid through the rupture would of course result in the failure of the entire hydraulic system.

United States Patent [1 1 Andrews [11] 3,733,969 [451 May 22,1973

[54] HYDRAULIC SYSTEM I [75] Inventor: Robert S. Andrews, St. Peters, Mo.

[73] Assignee: McDonnell Douglas Corporation, St. Louis County, Mo.

22 Filed: Mar. 15, 1971 21 Appl. No.: 124,327

Primary Examinerlrwin C. Cohen Attorney-Gravely, Lieder & Woodruff [5 7] ABSTRACT A hydraulic system has a high pressure supply line, a low pressure return line maintained at a pressure above the ambient pressure, and a plurality of subsystems connected between the supply and return lines. At least some of the subsystems individually include a selector valve and a hydraulically operated device. The selector valve is connected to the high pressure supply line and also to the return line, the latter connection being through a discharge line. The selector valve is also connected to the hydraulically operated device for diverting high pressure fluid thereto. A check valve is interposed in the discharge line for permitting fluid to flow from the discharge line to the return line, but not in the reverse direction, and consequently before fluid will flow past the check valve into the return line the pressure within the discharge line must equal that in the return line. Each subsystem of the foregoing nature further includes a shutoff valve which senses the return pressure in the discharge line and prevents high pressure fluid from being diverted to the hydraulically operated device when the pressure in the discharge line falls off. Accordingly, should the discharge line or any line in common with it rupture, the shutoff valve will close and the subsystem will be rendered inactive, thus preventing the loss of hydraulic fluid through the rupture when an attempt is made to operate selector valve of the ruptured subsystem. A substantial loss of hydraulic fluid through the rupture would of course result in the failure of the entire hydraulic system.

9 Claims, 4 Drawing Figures /0 30 //Z 6 #0 W /30 w H2 as are m /20 Q /3g 7 //a fro BACKGROUND OF THE INVENTION This invention relates in general to hydraulic systems and, more particularly, to a hydraulic system having shutoff means for protecting the system against the loss of fluid in the event of a rupture.

Most commercial and military aircraft have extensive hydraulic systems for operating much of the remotely controlled equipment on board. These hydraulic systems are normally divided in subsystems, and each subsystem controls and operates a different piece or grouping of equipment. For example, one subsystem may include hydraulic cylinders which when supplied with highpressure hydraulic fluid extend and retract the landing gear. Another subsystem may activate hydraulic cylinders connected to the flaps normally housed in the wings. Still another subsystem may operate a rotary hydraulic motor in the ammunition feed mechanism for a gun if the aircraft is of the military variety.

No matter what its purpose, a subsystem includes some type of hydraulically operated device and a selector valve for diverting high pressure fluid to the device. The selector valve is, of course, interposed between a hydraulic pump and the hydraulic device, and normally the low pressure fluid leaving the device returns to the selector valve and then through a return line common to many subsystems. Each subsystem return line is usually provided with a check valve at its juncture with the common return. The common return empties into a reservoir from-which the pump draws the fluid, and normally the reservoir and common return are pressurized relative to the surrounding atmosphere. For example, the hydraulic system at the discharge port of the pump may be at 3,000 psi, whereas at the reservoir and the common return may be at 50 psi.

Within each subsystem the operated equipment remains idle when no pressure differential exists across the hydraulically operated device of the subsystem, and this condition exists when the selector valve is in a socalled neutral position. Notwithstanding its ability to balance pressures across the hydraulic device when in the neutral position, leakage inherently occurs across the lap fits of selector valves, and the leakage passes into the return line of the subsystem and pressurizes that return line. The leakage has the effect of elevating the pressure of the subsystem return line to that of the reservoir so that normally no pressure differential of any significance exists across the check valve at the juncture of the subsystem return and the common return for all the subsystems.

Should a rupture occur in the portion of any subsystem located beyond the selector valve therein when that valve is in its neutral position, then fluid will leak from that portion and the return pressure therein will drop below the pressure of common return line and reservoir due to the presence of the check valve at the juncture of the subsystem return and the common return. The check valve will also prevent the loss of fluid from reverse flow so the entire system will remain pressurized and operative. However, once the selector valve in the ruptured subsystem is actuated, that is moved out of its neutral position, fluid will flow through the valve and that fluid will eventually leave the system through the rupture. Consequently, the high pressure fluid will not operate the hydraulic device, but instead will flow out of the system. Unless the selector valve is immediately returned to its neutral position, the fluid in the reservoir will be depleted to the extent that the entire hydraulic system becomes inoperative. In other words, a rupture in only one subsystem can cause the entire hydraulic system to fail.

SUMMARY OF THE INVENTION One of the principal objects of the present invention is to provide a hydraulic system which is composed of several subsystems and which will not fail when any of the subsystems are ruptured, but will only be rendered inoperative as to the ruptured subsystem. Another'object is to provide a hydraulic system which is suitable for use in commercial and military aircraft provided with hydraulically operated equipment. A further object is to provide a shutoff valve for preventing the flow of hydraulic fluid through a ruptured hydraulic subsystem so that the entire hydraulic system is not disabled due to a defective subsystem. Still another object is to provide a shutofl valve of the type stated which is extremely durable in construction and reliable in operation. These and other objects and advantages will become apparent hereinafter.

The present invention is embodied in a hydraulic system having a hydraulically operated device and shutoff means for sensing return pressure and for preventing the diversion of hydraulic fluid to the hydraulic device in the event the return pressure falls off. The invention is also embodied in the shutoff means itself. The invention also consists in the parts and in the arrangements and combinations of parts hereinafter described and claimed. 1

DESCRIPTION OF THE DRAWINGS In the accompanying drawings which form part of the specification and wherein like numerals refer to like parts wherever they occur:

FIG. 1 is a schematic view of a hydraulic system having several subsystems, each of which is provided with a return pressure operated shutoff valve for preventing the flow of high pressure fluid through the subsystem should a rupture on the return side of the subsystem occur;

FIG. 2 is a sectional view of a selector valve including a main directional control valve, a pilot valve for operating the control valve, and a return pressure operated shutoff valve which upon the loss or return pressure isolates the pilot valve from the high pressure fluid and prevents the pilot valve from operating the control valve, the shutoff valve being depicted as it would be with the entire hydraulic system at ambient pressure;

FIG. 3 is a sectional view of the return pressure operated shutoff valve showing it open when the system is.

pressurized; and

FIG. 4 is a sectional view of the return pressure operated shutofi' valve when the system is pressurized and the return pressure operated shutofi valve is closed due 1 to a drop in the return pressure of the subsystem.

DETAILED DESCRIPTION as well as in other applications. The system 2 includes a low pressure return line 4 leading up to and supplying hydraulic fluid to a reservoir 6, which in turn is connected to a pump 8 through a suction line 10. The pump 8 elevates the pressure of the fluid and discharges the high pressure fluid into a high pressure supply line 12. The pressure of the fluid in the return line 4, reservoir 6, and suction line 10 is termed the return pressure of the system 2, and, while this pressure is considerably below the pressure of the fluid in the supply 12, it is still above the ambient pressure external to the system2, primarily to prevent the pump 8 from cavitating. ln other words, the return line 4 and reservoir 6, and likewise the suction line 10, are all pressurized, but of course not nearly to the extent that the supply line 12 is. To pressurize the return line 4, and suction line 10, the reservoir 6 is provided with a piston 14 having large and small diameter faces. The large diameter face is exposed to-the interior of the reservoir and the fluid supplied thereto by the return line 4. On the other hand, high pressure fluid derived from the supply line 12, acts against the small diameter face, forcing the piston 14 against the fluid within the reservoir 6 and thereby pressurizing that fluid. Interposed between the supply line 12 and the return line 4 is a relief valve 18. Aside from the foregoing, the hydraulic system 2 also includes several. subsystems 20, 22 and 24 or more, each of which is connected between the high pressure supply line 12 and the low pressure return line 4. Accordingly, the supply line 12 and the return line 4 are common to all the subsystems 20, 22 and 24. Each subsystem possesses some type of hydraulically operated device. For example, if system 2 constitutes the hydraulic system of an aircraft, the device of the subsystem may operate the landing gears or flaps, while the device of the system 24 may extend the gun gas doors. The bydraulic device of the subsystem 22, on the other hand, may drive the mechanism for feeding ammunition to a gun. In a typical aircraft application the supply pressure, that is the fluid pressure in the high pressure common supply line 12, is maintained usually at about 3,000 psig, while the return pressure in the common return line 4 is usually maintained at about 50 to 100 pslg.

Broadly speaking, the hydraulic subsystem 20 includes (FIGS. 1 and 2) a solenoid selector valve 30 and a double acting hydraulic cylinder 32, the operation of which is dependent on high pressure fluid supplied through the selector valve 30. The cylinder 32 comprises a barrel 34 and piston 36 shiftable in the barrel 34. The piston 36, of course, carries a rod 38 through which force is transferred to the operated equipment. The interior of the barrel 34 at its ends is connected to the selector valve 30 through cylinder lines 40 and 42. The selector valve 30 is also connected to the high pressure supply line 12 through a feed line 44, and to the low pressure return line 4 through a discharge line 46. Near its juncture with the return line 4, the discharge line 46 is provided with a check valve 48 which allows fluid to flow from the discharge line 46 into the common return line 4, but not in the opposite direction.

The solenoid selector valve 30 (FIG. 2) is in effect three valves integrated into a single housing 50. In particular, the selector valve 30 is composed of a pilot operated main directional control valve 52, a pilot valve 54 for operating the main valve 52, and a return pressure operated shutoff valve 56 interposed between the main valve 52 and pilot valve 54 for preventing high pressure fluid from flowing to the pilot valve 54 in the event of a rupture or leak in any of the cylinder lines 40 and 42, the cylinder 32 or the discharge line 46, all of which are in common and constitute the return side of the subsystem 20 when the solenoid selector valve 52 in its neutral position, that is to say when it is not diverting high pressure fluid to the hydraulic cylinder 32. Actually, the shutofi valve 56 senses the return pressure in the subsystem 20 and when that pressure falls off, or in other words drops significantly below the return pressure in the low pressure common return line 4, it blocks the flow of high pressure fluid to the pilot valve 54 so that the pilot valve 54 will not operate the main control valve 52. This, in turn, prevents the diver.- sion of high pressure fluid through either of the cylinder lines 40 or 42, and the cylinder 32 does not operate, at least from fluid supplied by the hydraulic system 2. Aside from being connected with the return pressure operated shutoff valve 56 the main directional control valve 52 and the pilot valve 54 are conventional. Heretofore main valves and pilot valves similar to the valves 52 and 54, respectively, have been integrated into the same housing and connected by ducting within such housings.

The main directional control valve 52 comprises (FIG. 2) a shiftable spool 60 which operates in a bore 62 located within the housing 50. The bore 62 is circumscribed by an annular center or high pressure chamber 64 which is centrally disposed between the ends of the bore 62 and is connected with the feed line 44 leading from the high pressure supply line 12. On each side of the center chamber 64 the bore 62 is ringed by annular cylinder chambers 66 and 68 which are connected to the cylinder lines 40 and 42, respectively. Beyond the cylinder chambers 66 and 68, the bore 62 is surrounded by annular return chambers 70 and 72, both of which are connected to the discharge line 46. Each annular chamber 64, 66, 68, 70 and 72 opens into the bore 62. At the ends of the bore 62 the housing is provided with end chambers 74 and 76 to which the end faces of the spool are exposed. Extending through both end chambers 70 and 72 are springs 78 which exert equal and opposite axially directed forces on the spool 60 and maintain it in a neutral or centered position in the bore 62. The spool 60 is configured such that when in its neutral or centered position it will isolate the ports leading from the high pressure chamber 64 and prevent high pressure fluid in that chamber from flowing axially through the bore 62. The spool 60 does, however, have a relieved portion 80 between the ports of the cylinder chamber 66 and the ports of the return chamber and likewise another relieved portion 81 between the ports of the cylinder chamber 68 and the ports of the return chamber 72 so that the cylinder lines 40 and 42 and the discharge line 46 will all be in common and at the same pressure when the spool 60 is in its neutral position. The relieved portion of the spool 60 is long enough to place the high pressure chamber 64 and the cylinder chamber 66 in communication when the spool 60 is shifted to the right in FIG. 2,' and in that case the other relieved portion 81 will be presented beyond both the cylinder chamber 68 and the return chamber 72. The return chamber 70, however, will be blocked. Consequently, when the spool 60 is shifted out of its neutral position and to the right, high pressure fluid will flow from the center chamber 64 into the bore 62 and thence into the cylinder chamber 66 and cylinder line 40. The increase in pressure will be transmitted to one end of the cylinder barrel 34, causing the piston 36 to move therein. As the piston 36 moves it displaces fluid from the barrel 34 and this fluid flows into the cylinder line 42 which discharges it into the other cylinder chamber 68. From the cylinder chamber 68 the fluid flows through the bore 62 and into the return chamber 72, from which it empties into the discharge line 46. When the spool 60 is shifted to the left, the fluid in the center chamber 64 and cylinder chamber 68 are placed in communication and likewise so are the cylinder chamber 66 and the return chamber 70, thus enabling the fluid from the feed line 44 to flow through the selector valve 52, the lines 40 and 42 and the hydraulic cylinder 32 in the opposite direction. The reversal of flow, of course, causes the piston 36 to move in the opposite direction through the barrel 34 of the cylinder 30.

The end chambers 74 and 76 are connected with the pilot valve 54 through internal passageways 82 and 84, respectively, which are also disposed in the housing 50. The center chamber 64, on the other hand, is connected with the return pressure operated shutoff valve 56 through a high pressure connecting port 86, and likewise the return chamber 70 is connected with the shutoff valve 56 through a channel 88.

The shutoff valve 56 and the pilot valve 54 possess (FIG. 2) a common feed port 90 which leads from the former to the latter and when the shutoff valve 56 is open forms a continuation of the connecting port 86. The pilot valve 54 further includes a pair of solenoids 92 and 94, the coils of which are connected across a suitable electrical energy source through a switch located remote from the solenoid selector valve 30. The pilot valve 56 is conventional in construction and its sole purpose is to divert high pressure fluid from the feed port 90 to either one of the passageways 82 or 84. If the solenoid 92 is energized, the connecting port 90 will be placed in communication with the passageway 82, and this will increase the pressure in the end chamber 74, causing the spool 60 to move to the right (FIG. 2), provided of course that the shutoff valve 56 does not block the normal connection between the connecting port 86 and the feed port 90. Conversely, when the solenoid 94 is energized the connecting port 90 and the passageway 84 as well as the end chamber 76 are placed in communication, causing the spool 60 to shift to the left.

The return pressure operated shutoff valve 56 is interposed between the main control valve 52 and the pilot valve 54, and more specifically between the connecting port 86 extending from the former and the feed port 90 leading into the latter. Indeed, the connecting port 86 may be considered the high pressure inlet port to the shutoff valve 56 and the feed port 90 may be considered the outlet port of the shutoff valve 56. Under normal operating conditions the shutoff valve 56 provides communication between the ports 86 and 90, but should the pressure in the discharge line 46 or the cylinder lines 40 or42 drop'significantly, the shutoff valve 56 will sense a decrease in pressure and will block the connecting port 86. Of course, when the port 86 is blocked, the spool valve 60 will not move upon energizing either of the solenoids 92 and 94, as feed port 90 is connected to the discharge line 46 and the return side of the hydraulic system 2.

The return pressure operated shutoff valve 56 comprises (FIG. 2) a large diameter valve cylinder bore 100 and a smaller diameter valve bore 102 formed in the housing 50. One end of the cylinder bore 100 opens into the bore 102, while theopposite end is vented through an aperture 104 to the surrounding atmosphere which is at ambient pressure. The connecting port 86 extending from the annular center chamber 64 and the feed port leading to the pilot valve 54 open into the bore 102 in axially offset relation to one another with the latter being closer to the cylinder bore than the former. Finally, the channel 88 leading from the return chamber 70 opens into the end of the bore 102 located remote from the cylinder bore 100.

The valve cylinder bore 100 and the valve bore 102 receive a valve element 106 composed of a piston 108 disposed within the cylinder bore 100 and a spool 110 disposed largely within the bore 102. The spool 110 is connected to the piston 108. The piston 108 is provided with an O-ring or other suitable seal 112 which wipes the surface of the cylinder bore 100, whereas the sides of the spool 110 are lapped into the valve bore 102. The entire valve element 106 is urged to a closed position (FIG. 2), that is a position in which the piston 108 is presented close to the end of the bore 102, by means of a spring 114 which is interposed between the opposite end of the cylinder bore 100 and the piston 108.

Externally, the spool 110 is provided with an end relief 116 located adjacent to the piston 108 and a center relief 118 which is spaced from the end relief 116 by a spool land and is disposed generally midway between the ends of the spool 110. When the valve element 106 is in its closed position (FIG. 2) the end relief 116 extends from the interior of the cylinder bore 100 to at least the feed port 90 leading to the pilot valve 54, but not to the connecting port 86 which is spaced axially from the port 90. The center relief 118, on the other hand, will be disposed at the connecting port 86 which leads from center annular chamber 64 of the main control valve 52. Thus, when the valve element 106 assumes its closed position, the center relief 118 will be at the supply pressure, but the end relief 116 will not.

Internally, the spool 110 is provided with an elon gated bore 120 which is disposed centrally therein and extends axially. At its one end the bore 120 opens into a poppet cylinder bore 122 which is located at and opens out of the free end of the spool 110, that is the end located remote from the piston 108. The elongated bore 120 houses a ball 124 and a coil-type spring 126 which urges the ball 124 toward the poppet cylinder bore 122. At the juncture of the elongated bore 120- and the poppet cylinder bore 122, the spool 110 is fitted with an orifice insert 128 having an orifice which terminates at a seat 130 exposed to the bore 120, and this seat is configured to form a fluid-tight seal with theball 124 when engaged by the ball 124. The elongated bore 120 communicates with the center relief 118 through a hole 132 which is disposed immediately beyond the seat 130.

The poppet cylinder bore 122 communicates with the end relief 1 16 through an axially extending passageway 134 in the spool 110, and that passageway equalizes the fluid pressure at both ends of the spool 110. Fitted into the poppet cylinder bore 122 is a poppet 136 having a fluted flange 138 at its forward end. The

flange 138 engages the surface of the cylinder bore 122 and guides the poppet 136 as it moves in the cylinder bore 122, but the flutes therein do not block the end of the axially extending passageway 134 so that the fluid in the passageway 134 remains at the same pressure as the fluid in the poppet cylinder bore 122. While the forward end of the poppet 136 is guided by the flange 138 the opposite end fits into and is guided within a bushing 140 set into the end of the spool 110.

The poppet 136 is hollow, having an internal axially disposed cylinder bore 142, and fitted into that cylinder -bore 142 is a piston 144 having an elongated needle 146 which projects axially from it through the forward end of the poppet 136. The needle 146 furthermore aligns with the seat 130 of the orifice insert 128 and indeed will project through the seat 130 and into the elongated center bore 120. It can thus also act as a cleaning stem for the orifice in the insert 128. The piston 144 has axially extending apertures 148 in it for equalizing the fluid pressure on both of its sides. Also contained within the axially disposed cylinder bore 142 of the poppet 136 is a coil spring 150 which urges the piston 144 forwardly in the cylinder bore 142, that is toward the flange 138. The spring 150 allows the piston 144 and needle 146 to retract into the poppet 136 to a position in which the end of the needle 146 is disposed to the rear of the valve seat 130, even when the poppet 136 is disposed fully within the poppet cylinder bore 122. (FIG. 4). Compared with the other springs 114 and 126 in the shutoff valve 56, the spring 150 is weaker than the former and stronger than the latter. Finally, the poppet 136 is provided with radially and axially oriented apertures 152 to equalize the fluid pressures within the poppet cylinder bore 122 and the internal cylinder bore 142 and channel 88.

From the foregoing, it is apparent (FIGS. 2-4) that the valve element 106 shifts within the cylinder bore 100 and bore 102; that the ball 124 shifts axially within the elongated bore 120 of the spool 110 toward and away from the seat 130; that the poppet 136 shifts axially within the poppet cylinder bore 122 of the spool 110; and that the piston 144 moves axially within the internal cylinder bore 142 of the poppet 136, carrying the needle 146 along with it. When the valve element 106 is in its closed position (FIGS. 2 and 4), the end of the spool 110 located remote from the piston 108 will abut against the housing 50 at the end of the bore 102 and accordingly, the poppet 136 will be contained entirely or fully within the poppet cylinder bore 122. The needle 146 in such an instance may project through the insert orifice 128 and seat 130 (FIG 2) or it may be located entirely to the rear of the seat 130 (FIG. 4), its position depending on whether or not the ball 124 is held against the seat 130 by high pressure fluid within the elongated center bore 120. When the valve element 106 is in its open position (FIG. 3) the relief 118 is presented opposite both of the offset ports 86 and 90 and establishes communication between those ports.

When the hydraulic system 2 is at rest (FIG. 1), that is when the pump 8 is not operating, the fluid pressure in all the lines including the supply and return lines 12 and 4 will be equal and at ambient pressure. Moreover, the spool 60 of the main control valve 52 (FIG. 2) will assume its neutral position since the springs 78 will exert equal and opposite forces on it. Finally, the large spring 114 within the shutoff valve 56 will urge the valve element 106 to its closed position, and in that position the spool 110 will block the connecting port 86 so that the pilot valve 54 is isolated from the connecting port 86 leading away from the main control valve 52 and the high pressure feed line 44. It will also make the feed port leading to pilot valve 54 common to return through the passageway 134 in the spool 110. The coil spring 150 within the poppet 136, being stronger than the spring 126 within the elongated bore 120, will cause the needle 146 of the piston 144 to engage the ball 124 and hold it away from its seat 130.

Once the pump 8 is energized (FIG. 1), the pressure of the fluid in the supply line 12 will be elevated, and likewise so will the pressure in the common return line 4 due to the differential areas on the piston 108 within the reservoir 6. As previously noted the pressure within the supply line 12 will be considerably higher than the pressure within the return line 4, but both will be above the ambient or atmospheric pressure external to the system 2. The low pressure of the return line 4 will not be transmitted directly to the fluid within the discharge line 46 of the subsystem 20 due to the presence of the check valve 48 in that line, although the discharge line 46 will in a relatively short span of time reach the pressure of the return line 4 and the reservoir 6 as will be apparent hereinafter.

The high pressure from the supply line 12 is transmitted to the fluid in the feed line 44 (FIG. 2) which in turn elevates the pressure in the annular outer chamber 64 of the main control valve 52 and in the connecting port 86 leading to the shutoff valve 56, since all are in common. Inasmuch as the connecting port 86 is disposed opposite to the center relief 118 of the spool 110, the fluid in the center relief 118 will also rise to the pressure of the supply line 12. The high pressure, however, will not be immediately transmitted to the feed port 90 leading to the pilot valve 54, since the valve element 106, being in its closed position, isolates the connecting port 86 from the feed port 90.

The rise in pressure within the center relief 118 causes fluid to flow through the hole 132 in the spool 110, and into the elongated center bore 120, and then through the orifice in the insert 128. This elevation in 7 pressure is transmitted to the return fluid within the poppet cylinder bore 122 since the two communicate through the orifice insert 128 and seat 130, the axial apertures 148 of the internal piston 144, and the axial and radial apertures 152 in the poppet 136. In addition, the increase in pressure will be transmitted from the poppet cylinder bore 122 through the axial passageway 134 and end relief 116 in the spool 110 to the large valve cylinder bore in which the piston 108 is disposed. The pressure of the fluid within the poppet cylinder bore 122 and valve cylinder bore 100 will not rise above the pressure in the return line 4 since the poppet cylinder bore 122 communicates with the discharge line 46 through apertures 152, the channel 88, and return chamber 70, and the discharge line 46 emptying 'into the return line 4 through the check valve 48. Thus, for all intents and purposes, the poppet cylinder bore 122 and valve cylinder bore 100 form a common fluid cavity which remains at the pressure of the common re turn line 4.

The elevated pressure of the fluid within the poppet cylinder bore 122 and the valve cylinder bore 100 exerts an axially directed force on the valve element 106, and this force overcomes the force exerted on it in the opposite direction by the spring 114. Therefore, the valve element 106 moves toward the spring 114 (FIG. 3) and compresses the same. As the valve element 106 moves, the spring 126 expands within the bore 120,

keeping the ball 124 engaged with the end of the needle 146, and the force so exerted causes the back face of the poppet 136 to remain engaged with the end face of the valve bore 102. From a relative standpoint, the poppet 136 moves out of the spool 110. In time the seat 130 will pass beyond the end of the needle 146, and when this occurs the ball 124 will engage the seat 130 and prevent any more fluid from entering the poppet cylinder bore 122. Indeed, the high pressure fluid in the bore 120 will force the ball 124 tightly against the seat 130, creating a secure seal at the endof the elongated bore 120. The valve element 106 continues to its full open position (FIG. 3) and is retained in that position by the positive or return pressure maintained in the poppet cylinder bore 122 and the large valve cylinder bore 100. In this connection, it should be noted that the return pressure is maintained in the cylinder bores 122 and 100 by reason of the leakage along the lapped fits of the spool 60 and the bore 62 of the main control valve 52 (FIG. 2) as well as the leakage along the lapped spool 110 of the shutoff valve 56 itself. This leakage results in some of the high pressure fluid from the center chamber 64 and connecting port 86 being diverted into the return chambers 70 and 72 and the shutoff valve return channel 88, so as to maintain a constant but minimal flow across the check valve 48, and this of course means that the pressure behind the check valve 48 has to be as great as the pressure in the return line 4. Leakage of this nature is inherent in spool-type valves.

When the shutoff valve element 106 is in its open position (FIG. 3), the center relief 118 is disposed opposite to both the connecting port 86 leading away from the main control valve 52 and the feed port 90 leading to the pilot valve 54, and consequently the elevated pressure is transmitted through the shutoff valve 56 to the pilot valve 54. Should the solenoid 92 be energized high pressure fluid will flow through the connecting passageway 82 to the end chamber 74 and will force the spool 60 of the main control valve 52 toward the opposite end chamber 76. This, in turn, will present the relieved portion 80 on the spool 60 opposite to the high pressure center chamber 64 and the cylinder chamber 66, making lines 44 and common. 0n the other hand, the relieved portion 81 assumes a position opposite the cylinder chamber 68 and the return chamber 72, making lines 42 and 46 common. Accordingly, high pressure fluid from the feed line 44 will flow into the cylinder line 40 to the hydraulic cylinder 32, causing the piston 36 to move therein. The low pressure fluid displaced by the piston 36 flows into the cylinder line 42 to the cylinder chamber 68 and thence to the return chamber 72, which empties it into the discharge line 46. When the other solenoid 94 is energized, the spool 60 of the main control valve 52 is displaced in the opposite direction, and this, of course, will reverse the flow through the cylinder lines 40 and 42, causing the piston 36 to move back to its initial position.

In the event of a rupture in the discharge line 46 (FIG 1) or in either of the cylinder lines 40 or 42 or for that matter even in the barrel 34 of the hydraulic cylinder 32, fluid will flow out of the rupture and the return pressure in the subsystem 20 will revert to ambient pressure. This will occur by reason of the fact that the discharge 46 and the cylinder lines 40 and 42 are all in communication with one another through the bore 62 of the main control valve 52. In this connection, it should be noted that the relieved portion of the spool 60 connects the cylinder chamber 66 and return chamber 70 and the relieved portion 81 connects the cylinder chamber 68 and the return chamber 72 when the spool 69 is in its neutral position. Since the poppet cylinder bore 122 of the shutoff valve 56 is connected to the return chamber 70 of the main control valve 52 through the channel 88, the pressure of its fluid will drop to ambient conditions also, and likewise so will the pressure in the valve cylinder bore 100. With no pressure to hold the valve element 106 in its open position, the spring 114 will force the valve element 106 to its closed position (FIG. 4) so that the spool blocks the connecting port 86 and prevents the high pressure fluid from flowing into the pilot valve feed port 90. The center relief 118 of the spool 110, however, remains pressurized from the connecting port 86 and likewise so does the elongated bore 120 since it communicates with the relief 118 through hole 132. The elevated pressure of the fluid in the bore 120 keeps the ball 124 engaged tightly with the seat 130, so that as the valve element 106 moves to its closed position under the influence of the spring 114 and thereby forces the poppet 136 back into the poppet cylinder bore 122, the needle 146 is driven into the cylinder bore 142 within the poppet 136 (FIG. 4). In other words, the ball 124, being firmly engaged with the seat due to the extreme pressure difl'erential across it, will not allow the needle 146 to unseat it and project through the seat 130. On the contrary, it causes the needle 146 and the piston 144 which carries that needle to retract into the cylinder bore 142 in the poppet 136 and compress the spring in that cylinder bore 142. Consequently, should a rupture occur in the lines 40, 42 or 46, high pressure fluid from the center relief 118 will not leak into the poppet cylinder bore 122 and thereafter leave the subsystem 20 through the rupture.

Since the connecting port 86 leading to the pilot valve 54 is blocked at the shutoff valve 56 and pilot port 90 is connected to return, when the return pressure of the subsystem 20 (FIG. 1) reverts to the ambient pressure, the spool 60 of the main control valve 52 will not move when either of the solenoids 90 or 92 is energized. This prevents fluid from being pumped out of the hydraulic system 2 through the rupture when an attempt is made to utilize the subsystem 20. As a result the hydraulic fluid reservoir 6 is not depleted and the remaining subsystems 22 and 24 as well as others will continue to operate. 1

When the hydraulic system 2 (FIG. 1) is deactivated, that is when the pump 8 is shut down, the pressure in the supply and return lines 12 and 4 equalizes and likewise so does the pressure across the seat 130 in the shutoff valve 56. This enables the spring 150 in' the poppet 136 to force the needle 146 through the orifice insert 128 and seat 130 and unseat the ball 124 therefrom (FIG. 2), since the spring 150 is stronger than the spring 126 on the opposite side of the ball 124.

From the foregoing, it is apparent that the shutoff valve 56 senses the return pressure in the subsystem 20, and prevents operation of the main control valve 52 if that return pressure falls off. Of course, a drop in return pressure indicates a rupture in the return portion of the. subsystem 20. 1

In lieu of having the shutoff valve 56 incorporated into the selector valve, the subsystem 22 (FIG. 1) has the shutofi valve 56 located remotely from the selector;

valve 160 which is incorporated into a hydraulic motor package 162. This motor 162 may be a rotary piston hydraulic motor of the type used to feed ammunition to guns. The selector valve 160 has high pressure feed line 164 leading up to it and a low pressure discharge line 166 leading away from it. The discharge line E66 empties into the common return line 4 and near the juncture of the lines 4 and 166, the discharge line 166 is provided with a check valve 168 which allows fluid to flow into the return line 4, but not in the reverse direction out of the return line 4. The feed line 164 on the other hand is connected with the outlet port 90 of the shutoff valve 56, whereas the inlet port 86 of the shutoff valve 56 is connected with high pressure supply line 12.

Should the pressure in either feed line 164 or dis charge line 166 fall off, the pressure in the poppet cylinder bore 122 will also drop and the valve element 106 will prevent high pressure fluid from flowing from the supply line 12 to the feed line 164. For all intents and purposes, the shutoff valve 56 operates the same and performs the same function in the subsystem 22 as it does in the subsystem 20.

The subsystem 24 (FIG. 1) includes a selector valve 180 and a single acting hydraulic cylinder 182 connected to the selector valve 180 through a single cylinder line 184. The selector valve 180 receives high pressure fluid from the 'supply line 12 through a feed line 186 and discharges the fluid at low pressure through a discharge line 188 which empties into the common return line 4 through a check valve 190. Like the selector valve 30, the selector valve 180 is solenoid pilot operated and incorporates a main control valve, a solenoid pilot valve, and a return pressure operated shutoff valve in the same housing. While the shutofl valve is the same as the shutoff valve 56, the control valve and pilot valve are slightly different from the valves 52 and 54, respectively, since they control a single acting cylinder instead of a double acting cylinder. In any event, the differences are minor and do not require further description.

This invention is intended to cover all changes and modifications of the example of the invention'herein chosen for purposes of the disclosure which do not constitute departures from the spirit and scope of the invention.

What is claimed is:

1. In a fluid system including a pump, a fluid operated device, a control valve connected with the pump and the fluid operated device for directing high pressure fluid to the device, a discharge line connected with the control valve for returning fluid to the pump at low pressure after the fluid is discharged from the fluid operated device, and means for maintaining the fluid in the discharge line at a return pressure greater than the external pressure surrounding the system when the pump is in operation; the improvement residing in a shutoff valve for preventing high pressure fluid from flowing into the fluid operated device when the return pressure in the discharge line falls off, said shutoff valve comprising: a housing having a chamber connected with the discharge line such that the chamber is continuously in communication with the discharge line, whereby the fluid will enter the chamber and the fluid in the chamber will be at the return pressure; a valve element in the chamber, the valve element being shiftable between an open position wherein it allows the high pressure fluid to flow to the fluid operated device and a closed position wherein it prevents the high pressure fluid from flowing to the fluid operated device, the valve element having a face exposed to that fluid in the chamber which is at the return pressure, the face being oriented such that the fluid at the return pressure exerts a force on the element which tends to shift the element to its open position; a spring for exerting a force on the valve element in the opposite direction, the force exerted by the fluid at return pressure being greater than the force exerted by the spring, whereby the valve element remains in the open position as long as the fluid in the discharge line remains at the return pressure and wherein the shutoff valve further comprises a means for bleeding a limited amount of high pressure fluid to the cavity during start-up to move said valve element to its open position.

2. The structure according to claim 1 wherein the fluid operated device is connected to the control valve through at least one hydraulic line which is in communication with the discharge line when the control valve is not diverting high pressure fluid to the fluid operated device.

3. The structure according to claim 1 wherein the shutofl valve housing has a pair of high pressure ports which open into the chamber so that a portion of the chamber is also exposed to high pressure fluid; and wherein the valve element includes a piston portion on which the face exposed to the fluid at return pressure is disposed, and a spool portion which places the ports in communication when the valve element is in its open position and prevents communication between the ports when the valve element is in its closed position.

4. The structure according to claim 3 wherein said means for maintaining pressure in the discharge line includes a check valve positioned therein downstream from the shutofl' valve, the check valve being oriented to allow fluid to flow only away from the shutoff valve and toward the pump; wherein one of the two ports which opens into the chamber is directly in communication with the pump; wherein said means for bleeding high pressure fluid to said cavity during start-up includes a reduced passageway in said valve element and leading from the portion of the chamber exposed to the high pressure fluid from said one port to the portion of the chamber exposed to the fluid at the return pressure so that during start-up the high pressure fluid will pressurize the portion of the chamber normally occupied by the fluid at return pressure, whereby the valve element will move to its open position; and wherein the valve element carries means for blocking the reduced passageway when the valve element reaches its open position.

5. The structure according to claim 4 wherein the means for blocking the passageway comprises a valve seat located along the passageway and always presented toward the fluid at high pressure, a blocking element carried by the valve element and shiftable between blocked and unblocked positions, the blocking element being engaged with the valve seat when in the blocked position so as to prevent high pressure fluid from flowing into the portion of the chamber normally exposed to the fluid at return pressure, and being located away from the valve seat when in the unblocked position so that high pressure fluid can pressurize the portion of the chamber normally occupied by fluid at the return pressure; and means for maintaining the blocking element in its unblocked position when the pump is not operating and the fluid pressure throughout the system is substantially equal.

6. The structure according to claim wherein the means for maintaining the blocking element in its unblocked position includes a needle which is shiftable relative to the valve element in the direction the valve element shifts, the needle being capable of projecting through the portion of the reduced passageway in which the valve seat is disposed and beyond the valve seat to hold the blocking element away from the valve seat.

7. The structure according to claim 6 wherein the means for blocking the passageway further includes a first spring urging the blocking element toward the valve seat and a second spring urging the needle toward and against the blocking element, the second spring being stronger than the first spring, whereby the blocking element will remain against the valve seat with the additional force of the high pressure fluid exerted against it.

8. The structure according to claim 7 wherein the means for blocking the passageway further includes a poppet housed within the valve element and shiftable relative thereto in the direction of movement for the valve element; and wherein the needle projects from the poppet and is shiftable relative thereto, and the second spring is housed within the poppet.

9. In a hydraulic system including a source of high pressure fluid, a hydraulically operated motor device, a control valve connected to the source of hydraulic fluid and to the hydraulic device for diverting high pressure fluid to the device so as to operate the device, a discharge line leading away from the control valve for returning the fluid to its source, and means for maintaining the fluid in the discharge line at a return pressure greater than the ambient pressure surrounding the system; the improvement comprising a shutoff valve for sensing the return pressure in the discharge line and for preventing the diversion of high pressure fluid to the hydraulic device when the return pressure falls off, said shutoff valve comprising: a housing having a cavity connected with-the discharge line so that'fluid in the cavity is at substantially the same'pressure as fluid in the discharge line, a high pressure inlet port in the housing and connected with the source of high pressure fluid; a high pressure outlet port in the housing, a valve element in the housing, the valve element being shiftable between a closed position wherein it prevents high pressure fluid from flowing from the inlet port to the outlet port and an open position wherein it allows high pressure fluid to flow from the inlet port to the outlet port, the valve element having a face exposed to the cavity and pressurized discharge fluid therein, and the face being positioned such that the force of the fluid in the cavity urges the valve element to its open position, so that the valve element is actuated and held in its open position by force derived from the return pressure in the discharge line, the valve element further having a reduced channel therein for bleeding a limited amount of high pressure fluid to the cavity and a seat surrounding the reduced channel; a spring for exerting a force on the valve element in opposition to the force exerted on it by the fluid in the cavity, the force exerted by the spring normally being less than the force exerted by the fluid; a blocking element carried by the housing and being shiftable toward and away from the seat and engageable with the seat for blocking the reduced channel when so engaged, the seat being oriented such that the blocking element when engaged with it will be forced tightly against it by high pressure fluid derived from the inlet port; a poppet housed at least partially within the valve element and being shiftable relative thereto; a needle housed partially within the poppet for holding the blocking element away from the seat when the pressure in the cavity and the pressure in the inlet port are substantially the same as the ambient pressure so that during start-up high pressure fluid at the inlet port will elevate the pressure within the cavity and cause the valve element to move to its open position, the needle being shiftable relative to the poppet and to the valve element; and another spring carried by the poppet for biasing the needle toward the seat and the blocking element, the other spring being of less strength than the spring which acts upon the valve element in opposition to the pressurized fluid in the cavity. l 

1. In a fluid system including a pump, a fluid operated device, a control valve connected with the pump and the fluid operated device for directing high pressure fluid to the device, a discharge line connected with the control valve for returning fluid to the pump at low presSure after the fluid is discharged from the fluid operated device, and means for maintaining the fluid in the discharge line at a return pressure greater than the external pressure surrounding the system when the pump is in operation; the improvement residing in a shutoff valve for preventing high pressure fluid from flowing into the fluid operated device when the return pressure in the discharge line falls off, said shutoff valve comprising: a housing having a chamber connected with the discharge line such that the chamber is continuously in communication with the discharge line, whereby the fluid will enter the chamber and the fluid in the chamber will be at the return pressure; a valve element in the chamber, the valve element being shiftable between an open position wherein it allows the high pressure fluid to flow to the fluid operated device and a closed position wherein it prevents the high pressure fluid from flowing to the fluid operated device, the valve element having a face exposed to that fluid in the chamber which is at the return pressure, the face being oriented such that the fluid at the return pressure exerts a force on the element which tends to shift the element to its open position; a spring for exerting a force on the valve element in the opposite direction, the force exerted by the fluid at return pressure being greater than the force exerted by the spring, whereby the valve element remains in the open position as long as the fluid in the discharge line remains at the return pressure and wherein the shutoff valve further comprises a means for bleeding a limited amount of high pressure fluid to the cavity during startup to move said valve element to its open position.
 2. The structure according to claim 1 wherein the fluid operated device is connected to the control valve through at least one hydraulic line which is in communication with the discharge line when the control valve is not diverting high pressure fluid to the fluid operated device.
 3. The structure according to claim 1 wherein the shutoff valve housing has a pair of high pressure ports which open into the chamber so that a portion of the chamber is also exposed to high pressure fluid; and wherein the valve element includes a piston portion on which the face exposed to the fluid at return pressure is disposed, and a spool portion which places the ports in communication when the valve element is in its open position and prevents communication between the ports when the valve element is in its closed position.
 4. The structure according to claim 3 wherein said means for maintaining pressure in the discharge line includes a check valve positioned therein downstream from the shutoff valve, the check valve being oriented to allow fluid to flow only away from the shutoff valve and toward the pump; wherein one of the two ports which opens into the chamber is directly in communication with the pump; wherein said means for bleeding high pressure fluid to said cavity during start-up includes a reduced passageway in said valve element and leading from the portion of the chamber exposed to the high pressure fluid from said one port to the portion of the chamber exposed to the fluid at the return pressure so that during start-up the high pressure fluid will pressurize the portion of the chamber normally occupied by the fluid at return pressure, whereby the valve element will move to its open position; and wherein the valve element carries means for blocking the reduced passageway when the valve element reaches its open position.
 5. The structure according to claim 4 wherein the means for blocking the passageway comprises a valve seat located along the passageway and always presented toward the fluid at high pressure, a blocking element carried by the valve element and shiftable between blocked and unblocked positions, the blocking element being engaged with the valve seat when in the blocked position so as to prevent high pressure fluid from flowing into the portion of the chamber normally exposed To the fluid at return pressure, and being located away from the valve seat when in the unblocked position so that high pressure fluid can pressurize the portion of the chamber normally occupied by fluid at the return pressure; and means for maintaining the blocking element in its unblocked position when the pump is not operating and the fluid pressure throughout the system is substantially equal.
 6. The structure according to claim 5 wherein the means for maintaining the blocking element in its unblocked position includes a needle which is shiftable relative to the valve element in the direction the valve element shifts, the needle being capable of projecting through the portion of the reduced passageway in which the valve seat is disposed and beyond the valve seat to hold the blocking element away from the valve seat.
 7. The structure according to claim 6 wherein the means for blocking the passageway further includes a first spring urging the blocking element toward the valve seat and a second spring urging the needle toward and against the blocking element, the second spring being stronger than the first spring, whereby the blocking element will remain against the valve seat with the additional force of the high pressure fluid exerted against it.
 8. The structure according to claim 7 wherein the means for blocking the passageway further includes a poppet housed within the valve element and shiftable relative thereto in the direction of movement for the valve element; and wherein the needle projects from the poppet and is shiftable relative thereto, and the second spring is housed within the poppet.
 9. In a hydraulic system including a source of high pressure fluid, a hydraulically operated motor device, a control valve connected to the source of hydraulic fluid and to the hydraulic device for diverting high pressure fluid to the device so as to operate the device, a discharge line leading away from the control valve for returning the fluid to its source, and means for maintaining the fluid in the discharge line at a return pressure greater than the ambient pressure surrounding the system; the improvement comprising a shutoff valve for sensing the return pressure in the discharge line and for preventing the diversion of high pressure fluid to the hydraulic device when the return pressure falls off, said shutoff valve comprising: a housing having a cavity connected with the discharge line so that fluid in the cavity is at substantially the same pressure as fluid in the discharge line, a high pressure inlet port in the housing and connected with the source of high pressure fluid; a high pressure outlet port in the housing, a valve element in the housing, the valve element being shiftable between a closed position wherein it prevents high pressure fluid from flowing from the inlet port to the outlet port and an open position wherein it allows high pressure fluid to flow from the inlet port to the outlet port, the valve element having a face exposed to the cavity and pressurized discharge fluid therein, and the face being positioned such that the force of the fluid in the cavity urges the valve element to its open position, so that the valve element is actuated and held in its open position by force derived from the return pressure in the discharge line, the valve element further having a reduced channel therein for bleeding a limited amount of high pressure fluid to the cavity and a seat surrounding the reduced channel; a spring for exerting a force on the valve element in opposition to the force exerted on it by the fluid in the cavity, the force exerted by the spring normally being less than the force exerted by the fluid; a blocking element carried by the housing and being shiftable toward and away from the seat and engageable with the seat for blocking the reduced channel when so engaged, the seat being oriented such that the blocking element when engaged with it will be forced tightly against it by high pressure fluid derived from the inlet port; a poppet housed at Least partially within the valve element and being shiftable relative thereto; a needle housed partially within the poppet for holding the blocking element away from the seat when the pressure in the cavity and the pressure in the inlet port are substantially the same as the ambient pressure so that during start-up high pressure fluid at the inlet port will elevate the pressure within the cavity and cause the valve element to move to its open position, the needle being shiftable relative to the poppet and to the valve element; and another spring carried by the poppet for biasing the needle toward the seat and the blocking element, the other spring being of less strength than the spring which acts upon the valve element in opposition to the pressurized fluid in the cavity. 